1. Field of the Invention
The present invention relates to a liquid crystal alignment film composition for forming an alignment film that vertically aligns liquid crystal, a liquid crystal device and a display apparatus.
2. Description of the Related Art
Liquid crystal display devices employing a twisted nematic mode are widely used as one type of liquid crystal devices. Development has actively proceeded in recent years on liquid crystal display devices employing a vertical alignment mode in which liquid crystal molecules having negative dielectric anisotropy resulting in superior viewing angle dependence and contrast ratio are aligned perpendicular to a substrate such that the liquid crystal molecules are activated in parallel with the substrate by application of a voltage.
Examples of methods for aligning liquid crystal molecules perpendicular to a substrate are disclosed in which a liquid crystal alignment film composed of a polyimide is provided on an ITO side of a glass substrate (Japanese Patent Application Laid-Open (JP-A) Nos. 2001-305549, 2001-311080, 2002-323701 and 2003-295194). These methods form a vertical alignment film by applying a solution, prepared by dissolving a polyamic acid and the like in an organic solvent, with a spinner or the like followed by imidization of the coat by heat treatment at 120° C. to 250° C. and rubbing treatment using a felt cloth or the like to impart a vertical alignment ability.
In addition, a method has been disclosed that uses a polyimide resin material for non-rubbing vertical alignment that aligns liquid crystal molecules perpendicular to a substrate by a non-rubbing method (JP-A No. 2006-516757). In this method, a vertical alignment film is formed by applying a polyamic acid by spin coating followed by preliminarily firing a substrate at 100° C. for 30 minutes and imidizing by firing at 250° C. for 1 hour.
Moreover, a method has been disclosed for providing a vertical alignment film by using a liquid crystal alignment agent composed of a polyamic acid and the like having a conjugated enone structure (JP-A No. 2003-114437). In this method, a vertical alignment ability is imparted by applying a solution containing an alignment agent dissolved in an organic solvent by the use of a spinner or the like, followed by imidization by heat treatment at 150° C. to 250° C. and irradiation with ultraviolet light with a wavelength of 320 nm to 450 nm.
However, in the case TFTs and interconnections are formed on the substrate surface, a liquid crystal alignment film formed according to the methods described above had the problem of preventing the obtaining of a liquid crystal alignment film with uniform thickness due to the occurrence of coating unevenness attributable to the presence of irregularities over the substrate surface.
In addition, since heat treatment is carried out at 120° C. to 250° C. after coating with a spinner or the like, these methods had the problem of preventing the substrate from being applied to substrates other than glass substrates in the form of flexible, general-purpose plastic films.
Moreover, in the case of expressing an alignment ability by a rubbing method, uneven rubbing occurs due to the presence of irregularities in the substrate surface, thereby resulting in uneven alignment and causing the problem of the occurrence of disturbances in liquid crystal alignment.
In addition, rubbing methods involving rubbing an alignment film with a rubbing cloth are susceptible to the generation of static electricity and fine debris while also making TFT susceptible to damage, thereby resulting in the occurrence of display defects.